In a typical ultrasonic transducer array, each transducing unit cell, sometimes known as a subelement, in the array is conductively connected to one another so that they may all be simultaneously driven as one acoustic element. To focus such an array, it is conventional to make use of a lens. The lens can be made of organic polymer akin to rubber, e.g. Room-Temperature-Vulcanizing (RTV) silicone elastomers. During the assembly process of the transducer array, this polymer needs to be cured to turn into a durable form thanks to the addition of sulfur. This process needs to be tightly controlled, often requiring manual manipulation by a human operator. The overall process is thus time consuming and expensive.
An acoustic element is made up of an array of transducing unit cells. Each individual transducing unit cell includes a pair of plates or electrodes, at least one in each pair being deformable so as to move reciprocally closer to and further from the other in the pair. This movement creates the acoustic signal. An acoustic transducer chip may include many acoustic elements juxtaposed to form the long axis of the chip in azimuth. The short axis of the chip is the elevation axis, which extends across the transducing unit cells in an array within an acoustic element.
Focusing or beam steering an acoustic transducer chip in azimuth is accomplished by adjusting the time delay for each signal sent to or received from each of the acoustic elements on the chip. The electronics may thus be used to shape or steer the beam. U.S. Pat. No. 7,087,023 (Daft et al.) illustrates how electronics can be used to focus an acoustic transducer array in elevation. The arrays are configured so that the DC bias can be separately applied to the transducers at any given row in elevation. A pattern of positive and negative bias voltages applied to different elevation rows can be used to create a desired focal zone in elevation.